1. Field of the Invention
The present invention relates to a method for producing a rubber composition containing natural rubber (NR), chloroprene rubber (CR) and carbon black (CB), using a kneading machine.
2. Description of the Related Art
Hitherto, in order to attain the vulcanization and the reinforcement of a rubber, an improvement in the function thereof, and the like, a rubber composition has been used in which sulfur, a filler and various chemicals are added to a rubber component. In general, however, powdery are many of sulfur, fillers such as carbon black and silica, and various chemicals such as zinc oxide and an anti-ageing agent. Thus, when these components are blended with a rubber component and the blend is kneaded, these components become into dust to be scattered, so as to cause, for example, problems that a weighing precision thereof is declined and the working environment is deteriorated. About, in particular, the fillers such as carbon black and silica, the ratio of the use amount thereof to that of the rubber component is large. Thus, when the fillers are blended into the rubber composition, it is important to blend the fillers with the rubber component as precisely as possible while the working environment is kept good.
As a method for solving this problem, there is known a technique of blending only a filler beforehand with a rubber component to prepare a master batch. JP-A-2008-179717 describes a technique of using natural rubber or styrene butadiene rubber as a binder component, and blending carbon black with this component to prepare a master batch.
However, the technique described in JP-A-2008-179717 discloses only a technique of making a specific rubber species, such as natural rubber or styrene butadiene rubber, into a master batch. Thus, JP-A-2008-179717 neither describes nor suggests that a master batch technique is used for a rubber composition in which natural rubber and chloroprene rubber are together used, so as to improve carbon black in dispersibility in this composition.